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Investigation of the copolymerization of butyl acrylate (BA) with vinyl neononanoate (VeoVA-9)
Get PDFThesis (MSc) -- University of Stellenbosch, 2006.ENGLISH ABSTRACT: This study has the goal of illuminating structure-properties relationships for copolymers of
vinyl neononanoate (VeoVa-9) and butyl acrylate (BA). The VeoVa-9/BA copolymers were
prepared using solution free radical copolymerization and miniemulsion copolymerization.
The free radical copolymerization of VeoVa-9/BA at different feed ratios in benzene at 80°C
using 2,2'azobis (2-methylpropionitrile) (AIBN) as initiator was investigated. The tenninal
model was used to describe the copolymerization of these monomers and the copolymer
composition was detem1ined using I H NMR spectroscopy. The reactivity ratios, estimated
using the nonlinear least square method, and the 95% confidence interval giving values of the
reactivity ratios, which were 0.042 (±0.014) and 6.95 (-0.53 /+0.65) for the VeoVa-9 and BA
respectively. The copolymerization kinetics for the VeoVa-9/BA was investigated by
following individual monomer consumption rates by in-situ NMR. The use of this method
provides useful information about the individual monomer concentration during the course of
reaction. The copolymerization reaction shows a higher tendency for BA to react than the
VeoVa-9.
The copolymerization of these monomers was also investigated in a heterogeneous system
using the miniemulsion technique. In these investigations the effect of surfactant, initiator
type and water solubility of the monomer on the batch and semi-batch miniemulsion
behaviour was demonstrated. The rate of the miniemulsion polymerization increased with
increasing surfactant concentration, while the final particle size of the latex decreased with
increasing surfactant concentration in the miniemulsion mixture. Two types of initiators were
used, water and oil-soluble initiators (ammonium persulphate (APS) and AIBN respectively).
The rate of the batch miniemulsion polymerization showed dependency on the type of
initiator used as the monomer conversion increased faster with APS than when using AIBN.
The average final particle size was also larger when the AIBN was used than it was when the
APS was used. The batch miniemulsion showed an increase in the nucleation (inhibition)
period and a slower polymerization rate as the VeoVa-9 concentration increased. The increase
in the VeoVa-9 concentration in both batch and semi-batch miniemulsions also led to an
increase in the particle size.
The obtained copolymers were characterized in terms of their chemical composition via
two-dimensional chromatography (2-D), and in tern1s of some of their physical properties
using dynamic mechanical analysis (DMA) and contact angle measurement. The 2-D analysis
showed that all the BA was incorporated in the copolymer; this result was also confinned by
IH NMR. The 2-D analysis also showed that the copolymer composition depends on the
monomer addition mode in the semi-batch process. The copolymer glass transition
temperature (Tg) value showed an increase as the VeoVa-9 concentration increased and the Tg
values of the copolymers ranged between the two homopolymers' Tg values. The
hydrophobicity of the copolymers increased as the VeoVa-9 concentration increased as was
indicated by contact angle measurements.AFRIKAANSE OPSOMMING:Die doel van die studie is om die struktuur-eienskap verhoudings vir kopolimere van
vinielneononanoaat (YeoYa-9) en butielakrilaat (BA) te bestudeer. Die YeoYa-9/BA
kopolimere was gesintetiseer deur van oplossingsvryeradikaalkopolimerisasie en miniemulsie
kopolimerisasie gebruik te maak. Die vryeradikaalkopolimerisasie van Yeo Ya-9/BA
met verkillende verhoudings YeoYa-9 tot BA in benseen, by 80°C, en met 2,2'azobis
(2-metielpropionitriel) (AIBN) as afsetter, was ondersoek. Die reaktiwiteitsverhoudings van
die monomere was skattings wat gemaak is deur van die terminale (endgroep)-model gebruik
te maak. Die kopolimeersamestellings was bepaal deur van IH-KMR-spektroskopie gebruik te
maak. Die reaktiwiteitsverhoudings, bepaal deur van die nie-lineere minste vierkantsmetode,
asook om van die 95% sekerheidsinterval gebruik te maak, was 0.042 (±0.014) en 6.95 (-0.53
/+0.65) vir Yeo Ya-9 en BA onderskeidelik. Die kopolimerisasiekinetika vir verskillende
YeoYa-9/BA verhoudings was ondersoek deur die individuele tempos van monomeeropname
d.m.v. in-situ KMR te volg. Hierdie metode verskaf nuttige inligting oor die konsentrasies
van individuele monomere gedurende die verloop van die reaksie. Die kopolimerisasiereaksie
dui op 'n hoer waarskynlikheid vir BA om te reageer as die YeoYa-9.
Die kopolimerisasie van hierdie monomere was ook ondersoek deur van 'n heterogene
sisteem gebruik te maak, in samewerking met die mini-emulsie tegniek. In hierdie
ondersoeke is die effek van die seep-tipe, inisieerder-tipe en die wateroplosbaarheid van die
monomeer op die lot- en op die semi-lot-mini-emulsie gedrag gedemonstreer. Die tempo van
die mini-emulsiepolimerisasie neem toe met toenemende seepkonsentrasie, terwyl die finale
partikelgrootte van die lateks dan afneem. Die twee tipes initieerders wat gebruik was, was
water- en olie-oplosbare initieerders (ammonium persulfaat (APS) en AIBN, onderskeidelik).
Die tempo van die lot mini-emulsiepolimerisasie het op die afhanklikheid van die tipe
initieerder gedui. Die monomeeromskakelingstempo was hoer wanneer APS gebruik was.
Die gemiddelde finale partikelgrootte was groter wanneer AIBN gebruik was. Die lot-miniemulsiepolmerisasie
het 'n toename in die inhibisie (inhibition/'nucleation')-periode getoon
en 'n stadiger polimerisasieternpo soos wat die YeoYa-9 konsentrasie toegeneem het.
'n Toename in YeoYa-9 se konsentrasie het ook 'n groter partikelgrootte tot gevolg gehad.
Die gesintetiseerde kopolimere is gekarakteriseer in terme van hul chemiese samestelling deur
twee-dirnensionele chromatografie (2-D), en in terme van sekere fisiese eienskappe, deur van
dinamiese rneganiese analise (DMA) en kontakhoekmetings gebruik te rnaak. Die 2-D
analises het gewys dat al die BA geinkorporeer was in die kopolirneer. Hierdie resultaat was
bevestig met 'H-KMR. Die 2-D analise het ook gewys dat die kopolirneersamestelling
afhanklik is van die addissiewyse in die semi-lot proses. Die kopolirneer se
glasoorgangstemperatuur (Tg) het toegeneern soos wat die konsentrasie van VeoVa-9
toegeneern het. Die Tg waardes van die kopolimere het gewissel tussen die van die twee
hornopolimere se Tg waardes. Die hidrofobisiteit van die kopolirnere het toegeneern narnate
die VeoVa-9 konsentrasie toegeneem het, soos ook aangedui deur kontakhoekmetings
Alternating hetero-arm copolymer molecular brushes as scaffolds for inorganic nano-wires
Get PDFThesis (PhD)--Stellenbosch University, 2013.ENGLISH ABSTRACT: This study describes the synthesis and self-assembly of hetero-arm molecular brushes (hetero-arm MBs). These MBs consist of two polymeric side chains (SCs) of different natures, alternatingly distributed along the main chain (backbone). Two different types of hetero-arm MBs were prepared: first, alternating amphiphlic hetero-arm MBs (AMBs), and second, alternating hetero-arm MBs (AHMBs). Hetero-arm AMBs were synthesized via two strategies: (I) via a combination of “grafting through” and “grafting onto”, and (II) via “grafting through”.
In approach (I), poly[vinyl benzyl (polyethylene glycol)-alt-N-alkyl-maleimide)] (poly[VB-(PEG12)-alt-N-(CnH2n+1)-MI]) was prepared via radical copolymerization of vinyl benzyl-terminated polyethylene glycol (VB-PEG12) with maleic anhydride (MAnh) (grafting through), which produces graft copolymers with PEG SCs and reactive succinic anhydride repeat units alternatingly distributed along the backbone. These graft copolymers were then modified by nucleophilic substitution (imidization) with alkyl amines (CnH2n+1-NH2) on the succinic anhydride residues (grafting onto). Three different primary amines possessing different alkyl chain lengths (n = 4, 12 and 16) were used in the modification process. In this way, hetero-arm AMBs with different hydrophilic to hydrophobic ratios were obtained.
In approach (II), similar hetero-arm AMBs were prepared in a one-step grafting through approach. In this case, poly[VB-(PEG17)-alt-N-(CnH2n+1)-MI] (n = 10, 16 and 20) was prepared via radical copolymerization of VB-PEG17 with N-dodecylmaleimide, N-hexadecylmaleimide and N-icosylmaleimide. Following the synthesis step, self-assembly of these hetero-arm AMBs in arm-selective solvents was investigated in relation to the alkyl chain length. The morphology of the obtained assemblies was characterized by Field Emission gun-Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM) and Fluorescence Microscopy (a fluorescent dye was encapsulated). Cylindrical-like aggregates, length 10 μm and diameter ~ 250 nm, were obtained upon hetero-arm AMBs self-assembly.
The second type of hetero-arm MBs was hetero-arm AHMBs, in which the SCs consist of PEG and poly(N,N-dimethylamino-ethyl methacrylate) (PDMAEMA). These hetero-arm AHMBs were prepared via a combination of grafting through and grafting from approaches. In this case, poly[vinyl benzyl-(polyethylene glycol)-alt-N-(poly(N,N-dimethylamino-ethyl methacrylate) maleimide] (poly[VB-(PEG17)-alt-N-(PDMAEMA)-MI) was prepared in the following steps: (1) alternating poly[vinyl benzyl-(polyethylene glycol)-alt-N-(4-hydroxyphenyl) maleimide] (poly[VB-(PEG17)-alt-N-(HPh)-MI]) was synthesized via radical copolymerization of VB-PEG17 with N-(4-hydroxyphenyl) maleimide (N-HPhMI). (grafting through), (2) the hydroxyl sites were esterified with 2-bromoisobutyryl bromide to afford poly [vinyl benzyl-(polyethylene glycol)-alt-N-(4-(2-bromobutyryloxy)phenyl) maleimide] (poly[VB-(PEG17)-alt-N-(BrPh)-MI]) (macroinitiator) and (3) an atom transfer radical polymerization (ATRP) reaction of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) was initiated from the obtained macroinitiator. This approach afforded poly[VB-(PEG17)-alt-N-(PDMAEMA)-MI] hetero-arm AHMBs with two water soluble SCs; however, one is water soluble at all pHs and temperatures (i.e. PEG), while the other is a pH- and temperature-sensitive polymer (i.e. PDMAEMA).
Initial attempts were made to fabricate cylindrical organo/silica hybrid materials based on these AMHBs as the organic template and tetra-ethylorthosilicate as the silica precursor. Preliminary results indicate the formation of silica nano-wires, ~ 8 μm in length and ~45 nm in diameter. The self-assembly behavior of these AHMBs in water at a temperature above the lower critical solution temperature of PDMAEMA (> 55 °C) was also investigated. Fibril morphology (~ 30 nm in diameter) was observed.
This study addresses initial attempts to fabricate organic/inorganic hybrid materials with controlled size and morphologies via densely grafted hetero-arm molecular brushes.AFRIKAANSE OPSOMMING: Hierdie studie beskryf die sintese en selfsamestelling van prototipe molekulêre borsels (prototipe MBs). Hierdie MBs bestaan uit twee polimeriese sykettings (SKs) van verskillende aard wat afwisselend langs die hoofketting (ruggraat) voorkom. Twee verskillende tipes van die prototipe MBs is gesintetiseer: eerstens, afwisselende amfifiliese prototipe MBs (AMBs), en tweedens, afwisselende hetero-arm prototipe MBs (AHMBs). Prototipe AMBs is gesintetiseer d.m.v. twee strategieë: (I) deur 'n kombinasie van „enting deur‟ en „enting aan‟ benaderings, en (II) deur middel van „n „enting deur‟ benadering.
In benadering (I) is poli[vinielbensiel(poliëtileenglikol)-alt-N-alkiel-maleïenamied)] (poli[VB-(PEG12)-alt-N-(CnH2n+1)-MI]) gesintetiseer deur radikaalkopolimerisasie van vinielbensiel-beëindigde-poliëtileenglikol (VB-PEG12) met maleïenanhidried („enting deur‟) wat entkopolimere produseer met PEG SKs en reaktiewe suksienanhidried herhaaleenhede wat afwisselend langs die ruggraat versprei is. Daarna is die entkopolimere gewysig d.m.v. nukleofiliese substitusie (imiedisering) met alkielamiene (CnH2n+1-NH2) op die oorblywende suksienanhidried („enting op‟). Drie verskillende primêre amiene met verskillende alkielkettinglengtes (n = 4, 12 en 16) is gebruik vir die wysigingsproses. So is prototipe AMBs met verskillende hidrofiliese tot hidrofobiese verhoudings verkry.
In benadering (II) is soortgelyke prototipe AMBs gesintetiseer in 'n een-stap „enting deur‟ benadering. In hierdie geval is poli[VB-(PEG17)-alt-N-(CnH2n+1)-MI] (n = 10, 16 en 20) gesintetiseer d.m.v. radikaalkopolimerisasie van VB-PEG17 met N-dodesiel maleïenamied, N-heksadesiel maleïenamied en N-ikosiel maleïenamied. Na afloop van die sintese stap is die selfsamestelling van hierdie prototipe AMBs in spesifieke oplosmiddels in verhouding tot die alkielkettinglengtes ondersoek. Die morfologie van die versamelings is gekarakteriseer deur veld-emissie-geweer-(Eng: field emission gun-)-skandeerelektronmikroskopie (FE-SEM), transmissie-elektronmikroskopie (TEM) en fluoresserende mikroskopie („n fluoresserende kleurstof is ingesluit). Silinderagtige versamelings (lengtes ~10 μm en deursnee ~250 nm) is deur die selfsamestelling van prototipe AMBs verkry. Die tweede soort prototipe MBs is prototipe AHMB, waarin die SKs uit PEG en poli(N,N-dimetielaminoetiel metakrilaat) (PDMAEMA) bestaan. Hierdie prototipe AHMBs is d.m.v. 'n kombinasie van „enting deur‟ en „enting van‟ benaderings gesintetiseer. In hierdie geval is poli[vinielbensiel-(poliëtileenglikol)-alt-N-(poli(N,N-dimetielaminoetiel metakrilaat) maleïenamied] (poli[VB-(PEG17)-alt-N-(PDMAEMA)-MI) gesintetiseer deur van die volgende stappe gebruik te maak: (1) sintese van afwisselende poli[vinielbensiel-(poliëtileenglikol)-alt-N-(4-hidroksifeniel) maleïenamied] (poli[VB-(PEG17)-alt-N-(HPh) -MI) deur midel van radikaalkopolimerisasie van VB-PEG17 met N-(4-hidroksifeniel) maleïenamied (N-HPhMI) („enting deur‟), (2) esterifikasie van die hidroksielgroepe met 2-bromoisobutiriel bromied om poli[vinielbensiel-(poliëtileenglikol)-alt-N-(4-(2-bromobutirieloksi) feniel) maleïenamied] (poli[VB-(PEG17)-alt-N-(BrPh)-MI]) (makro-afsetter) te berei, en (3) die atoomoordrag-radikaalpolimerisasie reaksie van 2-(N,N-dimetielamino)etiel metakrilaat (DMAEMA) wat begin is vanaf die gevormde makro-afsetter. Hierdie benadering gee poli[VB-(PEG17)-alt-N-(PDMAEMA)-MI] prototipe AHMBs met twee wateroplosbare SKs, waarvan een wateroplosbaar is by alle pHs en temperature (d.w.s. PEG), terwyl die ander tipe SK „n pH- en temperatuur-sensitiewe polimeer is (d.w.s. PDMAEMA).
Aanvanklike pogings is aangewend om silindriese organo/silika hibriedmateriale te sintetiseer, gebaseer op hierdie AHMBs as die organiese segment en tetraëtielortosilikaat as die silika voorloper. Die voorlopige resultate dui op die vorming van silikananodrade, lengte ~8 μm en deursnit ~45 nm. Die selfsamestellingsgedrag van hierdie AHMBs is ook in water ondersoek by 'n temperatuur hoër as die laer kritieke oplossingstemperatuur van PDMAEMA (> 55 °C). „n Draadagtige morfologie (deursnit ~30 nm) is waargeneem.
Hierdie studie beskryf aanvanklike pogings om organiese–anorganiese hibriedmateriale met beheerde groottes en morfologieë via dig-geënte hetero-arm molekulêre borsels te vervaardig.Doctora
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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